The present invention relates generally to a system for the comminution of coal and more particularly to an electrical interconnection for passing a current to an electrode within the high pressure, high temperature vessel of an explosive comminution system.
Explosive comminution of coal involves the heating and pressurization of a coal-water slurry within a vessel and the subsequent, rapid adiabatic expansion of the heated and pressurized slurry. One method of heating the slurry is electrical. An electrode, positioned within the vessel and submerged in the slurry, permits a current to pass through the slurry from the electrode to the vessel wall. The passage of current through the slurry produces, by resistance heating, a heated slurry.
The presently available apparatus for interconnecting an electrode to a power supply includes a single conductor extending through an opening in the vessel wall and terminating at the electrode. A ceramic seal closes the opening about the conductor.
These interconnection apparatus become unacceptable when the pressure within the vessel is raised above a predetermined level, e.g., above the critical pressure of the slurry liquid. The vessel pressure operates upon the conductor, creating a force imbalance which tends to push the conductor out of the vessel. The resulting stress on the ceramic seal causes deterioration and cracking thereof in a relatively short period of time.
The pressure imbalance problem is particularly acute in a large scale operation where large conductors are required. As the cross-sectional area of the conductor increases by a factor, the force required to maintain the conductor within the vessel increases in proportion to the square of the factor. Thus, if the area is increased twofold, the securing force must be increased fourfold.
In addition to having a tendency to crack when subject to stress, certain ceramic seals have a measurable permeability to fluids at a high pressure and temperature. With fluid permeation, the seal is substantially weakened and cracks therein develop more quickly.
Continuous cycling of the pressure and temperature conditions within the vessel further increases the likelihood of leakage and cracking. This is particularly true when the slurry is highly corrosive or chemically active. The present invention is designed to improve upon these and other aspects of providing an electrical connection to the interior of a high temperature, high pressure vessel.